*{margin:0;padding:0}

#box{
    position:absolute;
    top:50%;margin-top:-100px;
    left:50%;margin-left:-200px;
    width:400px;
    height:200px;
    background-color:#ccc;
}
#left-top{
     width:50px;
     height:50px;
     border-radius:0 0 50px 0;
     background-color: #FC0;
}
#right-bottom{
    width:50px;
    height:50px;
    border-radius:50px 0 0 0;
    background-color: #FC0;
    position:absolute;right:0;bottom:0px;
}
